1. Related Applications
This invention relates to our copending application Ser. No. 06/389,733 entitled "SHARED ENERGY SIGNALING APPARATUS", filed 18 June 1982.
2. Field of the Invention
This invention relates to a novel coder-decoder of the type employed in transmitting and receiving apparatus. More particularly, the present invention employs a purged code encoder for generating constant-weight unbalanced codewords containing error correction bits modulated with a balanced code set signal to provide a balanced code signal for transmission. The transmitted balanced code signal is demodulated and decoded to recover the original data signals.
3. Description of the Prior Art
The above-referenced copending application entitled "SHARED ENERGY SIGNALING APPARATUS" modulated the unbalanced raw data stream with a balanced code signal. However, this application did not explain the unbalanced data stream or attempt any explanation of how an error correction code could be employed at the transmitter end.
It is possible to add filler bits to a data stream to be transmitted in order to assure a data imbalance. Such filler bits are not related in any way to the data being transmitted, thus, the performance of the transmitting and receiving system is degraded because less power is available for each of the data bits. As an example of employing filler bits, it is possible to send sixteen bits of data and then to follow the data bits with eight filler bits of ones or zeros to achieve a desired unbalance. When the filler bits are added to achieve the unbalance, the block bits which comprise the designated group of bits may or may not have the desired unbalance even though the average unbalance of the data stream is achieved over a long period of transmission.
It is possible to impose an error correction code on the filled data stream bits which most likely would rebalance the data stream so that the desired unbalance is no longer achieved. Further, it would be possible to apply error correction bits to the original data bits before the filler bits are added to the error corrected data stream. Employing this technique, it is more likely that the desired unbalance would be achieved in the average of the data stream but this would not assure that the unbalance is uniform over desired blocks of data bits or over short periods of time.
When it is necessary to meet a particular requirement for unbalance in a data stream, it would be desirable to accomplish the unbalance by employing structure which is both simple and efficient.